Java 9+ Compatibility

[DennisRippinger]

When the Plugin is executed on a Java 9+ JVM a ClassCastException is thrown:

[ERROR] Could not add schema location to classpath
java.lang.ClassCastException: class jdk.internal.loader.ClassLoaders$AppClassLoader cannot be cast to class java.net.URLClassLoader (jdk.internal.loader.ClassLoaders$AppClassLoader and java.net.URLClassLoader are in module java.base of loader 'bootstrap')
    at com.phoenixnap.oss.ramlplugin.raml2code.plugin.SpringMvcEndpointGeneratorMojo.getSchemaLocation (SpringMvcEndpointGeneratorMojo.java:477)
    at com.phoenixnap.oss.ramlplugin.raml2code.plugin.SpringMvcEndpointGeneratorMojo.generateEndpoints (SpringMvcEndpointGeneratorMojo.java:261)
    at com.phoenixnap.oss.ramlplugin.raml2code.plugin.SpringMvcEndpointGeneratorMojo.execute (SpringMvcEndpointGeneratorMojo.java:521)
    [...]

The Plugin currently adds the Schema Location to the Classpath by getting the SystemClassLoader as an URLClassLoader, but because the underlying SystemClassLoader is no longer a URLClassLoader this results in an Error:

springmvc-raml-plugin/src/main/java/com/phoenixnap/oss/ramlplugin/raml2code/plugin/SpringMvcEndpointGeneratorMojo.java

Lines 492 to 499 in 6387072

	URLClassLoader urlClassLoader = (URLClassLoader) ClassLoader.getSystemClassLoader();
	Class<?> urlClass = URLClassLoader.class;
	Method method = urlClass.getDeclaredMethod("addURL", new Class[] { URL.class });
	method.setAccessible(true);
	method.invoke(urlClassLoader, new Object[] { new File(resolvedPath).toURI().toURL() });
	return "classpath:/"; // since we have added this folder to
	// the classpath this
	// should be used by the plugin

Several threads about this issue describe a workaround by further specifying the Class#forName usage, but as far as I understand this is not feasible for the current impl where it is assumed that the default classloader knowns the schema files.